Pythagorean Theorem: For any right angle, the sum of the squares of the lengths of the legs is equal to the square of the length of the hypotenuse.
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Triangle proportionality theorem- It a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally.

Converse of the triangle proportionality theorem- If a line divides two sides of a triangle proportionally, then it is parallel to the one side.

Side-Splitting theorem- A line parralel to one side of the trianngle divides the other two sides proportionally.
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Two-transversal proportionality corollary- three of more parallel lines divide two intersecting transversals proportionally.

Proportional Median Theorem- If two triangles are similar then their corresponding medians have the same ratio as their corresponding sides

Proportional Segments Theorem- An angle bisector of a triangle divides the opposite sides into two segments that have the same ratio as the other two sides
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Two-transversal proportional corally- three or more parallel lines devide the other sides proportional.